Quantum well materials for use in thermoelectric generators and other similar applications are comprised of a substrate bearing hundreds or thousands of alternating layers of two semiconductor materials having the same or similar crystalline structures, one semiconductor material serving as a barrier material and the other serving as a conducting material. Typical semiconductor pairs are silicon/silicon-germanium alloy (Si/SiGe), boron/boron-carbon alloy (B/B—C), two different boron-carbon alloys such as B4C/B9C, and silicon/silicon carbide (Si/SiC).
Conventional methods for depositing alternating layers of semiconductor pairs onto a substrate are thermal vapor deposition, electron beam deposition, molecular beam epitaxy and magnetron sputtering. Methods of depositing multiple layers of the pairs of materials from respective sources onto a reciprocated narrow tape-like substrate have been proposed. However, deposition is more usually performed with box coaters on static substrates of small size, for example, one foot square. These methods are very costly and are not scalable to large size substrates or to cost effective mass production of large quantities of quantum well materials.
The substrate employed in a quantum well material for thermoelectric applications is preferably a material having low thermal and electrical conductance. Silicon was often the material of choice for non-roll-to-roll coatings but Kapton® polyimide film for cost effective large scale production is preferred. However, in thermoelectric generators, the presence of a substrate in a quantum well material becomes a parasitic loss in the system. It would be desirable, if possible, to minimize this parasitic loss, preferably by eliminating the substrate altogether.
U.S. Pat. Nos. 5,814,367, 6,033,782 and 6,288,837, which are owned by the assignee of the present invention, disclose methods of making single and multi-layer magnetodielectric compositions, optical thin films and signature and energy control films and compositions with and without a supporting substrate.
U.S. Pat. Nos. 6,096,964, 6,096,965, 5,550,387, and 5,436,467 provide further background information in the use and theory of quantum well thermoelectrics.